While emphasizing the complex and subtle interplay among multiple brain chemicals, Fisher argues convincingly that dopamine deserves center stage. This neurotransmitter drives animals to seek rewards, such as food and sex, and is also essential to the pleasure experienced when such drives are satisfied. Fisher thinks that dopamine's action can explain both the highs of romantic passion (dopamine rising) and the lows of rejection (dopamine falling). Citing evidence from studies of humans and other animals, she also demonstrates marked parallels between the behaviors, feelings and chemicals that underlie romantic love and those associated with substance addiction.*

Romantic love, she contests, drove ancestral women and men to come together long enough to conceive, whereas attachment, another complex of feelings with a different chemical basis, kept them together long enough to support a child until weaning (about four years). Evidence indicates that as attachment grows, passion recedes. Thus, the same feelings that bring parents together often force them apart, as one or both fall in love with someone new. In this scenario, broken hearts and self-defeating crimes of passion become the unfortunate by-products of a biological system that usually facilitates reproduction.

One chapter is a litany to passion in other animals, a vivid reminder that we are not the only species that feels deeply.